Panasonic TC-L42U30 No Standby

[curt2199]

I've been trying to diagnose the problem with this power supply for a week or so and am struggling to find it. I've pulled several caps and they tested ok, have tested the bridge rectifier and have 168.5V DC out of it. I ended up finding a 470uf cap (right side of pic) in the standby power circuit that had been twisted on the board and was shorting. The solder on the cap looked factory and after untwisting it had a good 1/4" between the board and the bottom of the cap. I de-soldered and pushed it down on the board. I'm not sure how it ended up that way but I'm wondering if it killed other components when it shorted. after tracing the standby circuit it appears to go to the smaller yellow (transformer?) on the right center of the pic so I was assuming it was getting standby power out of that. I need help testing here because I get no voltage at the transformer out to the standby pins. There are two transformer pins that are showing 165V with arrows on the board pointing away from it and a few others that are showing very low voltage. I'm not sure if it's the transformer bad or something before that.

Also in an effort to help diagnose I applied 5v dc via an adapter to the standby circuit near the pin and in doing so when pushing the power button the power supply relay clicked on and off twice followed by the TV flashing the standby led 10 times.

[R_J]

Re: Panasonic TC-L42U30 No Standby

Check the voltages on ic201? its the 7 pin ic near the standby transformer, look up its number for the spec sheet to get the voltages, (NOTE: voltages on the HOT side are referenced to HOT Ground [D101 bridge rectifier negative]) but they do go bad quite often. Did you check F201 fuse?
Is the ic a STR-A6051M

[dskall]

Re: Panasonic TC-L42U30 No Standby

Your fuses are good? What is the number of that ic next to small transformer? May have pulled the leads out of the cap. I would check that it is good.

[curt2199]

Re: Panasonic TC-L42U30 No Standby

Ok, so I'm testing this with the board pulled and plugged in.

I had desoldered that IC already and resoldered. The IC is an a A6051m like mentioned.

Here are the values in reference to hot ground at the rectifier:

1:0
2:0
3:0
4:0.642V
5:5.09V

7:165.4V
8:165.4V

In testing those I tested the standby pin with hot ground and am seeing -4.8v... maybe that doesn't mean anything because went tested against the case or board ground I get 0V.

Also, I traced the 5V VSS out of that IC to several NEC 2581 components at the hot to cold line but they show very little to no voltage.

Also, I pulled the twisted cap and it checks out fine.

Check the voltages on ic201? its the 7 pin ic near the standby transformer, look up its number for the spec sheet to get the voltages, (NOTE: voltages on the HOT side are referenced to HOT Ground [D101 bridge rectifier negative]) but they do go bad quite often. Did you check F201 fuse?
Is the ic a STR-A6051M

[curt2199]

Re: Panasonic TC-L42U30 No Standby

Fuses good and cap is good.

Your fuses are good? What is the number of that ic next to small transformer? May have pulled the leads out of the cap. I would check that it is good.

[curt2199]

Re: Panasonic TC-L42U30 No Standby

ideas?

[dick_barton]

Re: Panasonic TC-L42U30 No Standby

If the voltage between pins 2 and 3 is 0V as you say, then you need to check carefully the values of the resistors in the resistance chain leading back to the main capacitor.